What is Innate Immunity

We hear about new kinds of bacteria, viruses and diseases every day. Some where someone has been affected by some disease. Your next door neighbor has a cold. Your aunt has cancer. Your friend had jaundice. You had chicken pox. Disease talk is everywhere. The truth is, disease is everywhere too. Tiny micrometer sized organisms are not the only ones that cause diseases though they are in the word’s truest sense, the culprits. Carried from one place to another in many different ways (by air, water, land, and organism) these tiny organisms called pathogens invade a host body and multiply in it. They take up the body’s nutrients and make the host weak. Sometimes the person survives, sometimes he dies.

What protects us from diseases?

Our ability to fight disease causing organisms is called immunity which is conferred to us by the immune system. We have two kinds of immunity- innate and acquired. Innate immunity is developed from the third month of gestation in the mother’s womb to the third month after the child is born. Acquired immunity comes into effect only after that time period.

What is Innate Immunity

The placenta is a connection formed between the foetus and mother by the third month of pregnancy. This thus becomes the sole link between the two bodies. The baby derives its nutrition from the mother’s system through it. Immunoglobin G (IgG) an antibody (agent to fight foreign bodies or antigens) is the first to be transported to the growing foetus. It is also the first immunity that a child receives.

After birth, doctors usually advise the parent to breast feed the child till a minimum age of three to six months. Not only is breast milk healthy for the baby, the milk produced initially is called colostrum and contains heavy quantities of an antibody called Immunoglobin A (IgA). The first three months of a child’s life after birth are most crucial. It is the time when the baby acclimatizes to the outside world. Survival is essential and for survival, immunity is essential which is conferred by colostrum’s immunoglobins. Within three months from birth, the child’s bone marrow and thymus gland mature. These contain cells called lymphocytes which help acquire immunity in later life.

Barriers provided by Innate immunity

Innate immunity is also called non-specific resistance as it provides general care and not action against a specific pathogen. It has six barriers for protection:

  • Physical or mechanical barriers
  • Chemical barriers
  • Phagocytosis
  • Fever
  • Inflammation
  • Acute phase proteins

innate immunity

Physical or mechanical barriers include the skin and mucous membrane. The outer epidermis and inner dermis layers of skin protect the body by shedding off any infected surface tissue. Skin is further covered by a keratin protein coat which hampers any microbial entry into the body via skin. Mucous membrane is present in the Respiratory system, Gastro-intestinal Tract and Urino-genital System. Here, the mucous helps trap pathogens and they are moved out of the body via cilliary muscle movement.

Chemical barriers include a wide range of self produced chemicals and adverse conditions. Parietal cells of the stomach secrete acids to reduce stomach pH to 2 so that pathogens are unable to find an ambient environment to reproduce. Sebaceous glands on skin secrete organic oil compounds to reduce overall skin pH.  Hydrolytic enzymes called lysozymes are present all over the body in various liquid secretions like tears and urine. They are particularly anti-bacterial. Interferons are chemicals released from an infected cell during a virus attack. They are released to make the healthy cells aware of the virus and to prepare the appropriate defense. Complement proteins are a chain of 9 proteins which are activated as a cascade for protection. They form a lytic complex and perform lysis of infected cell.

Phagocytosis is the act of engulfing of foreign matter by a protecting cell (macrophage).

Fever is the increase of body temperature to kill microbes in the body. Cytokines are released which act on the hypothalamus in the brain to cause this temperature change. Though fever is favorable for us, temperatures exceeding 100°F are treated with anti-pyretic drugs as at temperatures higher than this, our metabolic system may not work correctly.

Anti-microbial proteins are a thin protein layer which covers our skin and is about 1 micron thick. It is absent in 2% of the world population and is the most effective innate immunity surface pathogen barrier.

Inflammation signs are heat, erythema (redness of skin), edema (swelling) and pain. It is caused by physical, chemical and mechanical injuries. The action involves a complex cytokine induced WBC protective pathway.

Hepatocytes (liver cells) are induced by cytokines released at injured tissue site to secrete acute phase proteins. These are majorly of three types- CRP (C-reactive complement protein component), MBP (mannose binding metal protein) and BP (binding protein). They behave as opsonins and stimulate the complement activation pathway which releases anti-allergen hormones like histamine, serotonin, prostaglandins and bradykenin. These further help in fighting off infection.

Thus, this simple protective system helps in rescuing us from a number of diseases present around us. Immunity is the reason why we are sometimes affected by a disease and sometimes not. The lady next door has cough but you might not catch it if your immune system is strong enough. Any system in the body can be thoroughly maintained only via intake of proper nutrition and adequate exercise.